Physiologic responses to abrupt withdrawal of propranolol were examined in 14 normal subjects. Heart rate during exercise and upright tilt was slightly increased after propranolol when compared with prepropranolol performance. Platelet survival was shortened 22% after propranolol. However, heart rate response to isoproterenol, beta receptor function of white blood cells, and levels of plasma catecholamine were unchanged during propranolol withdrawal. Increased platelet deposition in coronary stenoses may play a role in ischemic sequelae abrupt propranolol withdrawal.